Deoxyribonuclease (Dnase) activity was described in bovine organs in the 1800s, and the proteins responsible for this activity have been characterized over the last century. In the early 1900s, digestion of nucleic acids by liver, spleen, pancreas, and other organs was investigated. As reviewed
[1], the enzymatic activity was given a succession of names, including desoxyribonuclease, and determined to function optimally at neutral pH
[2]. The founding member of the Dnase1 family, Dnase1, was isolated and crystallized in 1950
[1]. Dnase1 activity was generally recognized to require divalent cations (Ca
2+ or Mg
2+), to act optimally at neutral pH, and to leave 5′ phosphates following DNA cleavage
[1][2][3][4]. As reviewed
[5], in 1947 a second, “acid DNase” activity was described in mammals
[6]. Acid DNase activity had an ubiquitous tissue distribution and showed peak activity at acidic pH
[5]. To distinguish the acid DNase from the pancreatic DNase, which was called Dnase I, and later Dnase1, the term Dnase II (later Dnase2) was suggested as an alternative to acid DNase
[3]. Dnase2 has no requirement for divalent cations and hydrolyzes double stranded DNA into short oligonucleotides bearing 3′ -phosphate groups
[5]. Multiple proteins possess acid and neutral DNase activity. The Dnase II/Dnase2 family now consists of Dnase2a, Dnase2b, and L-Dnase II/SerpinB1
[7]. In the 1990s, three new members of the Dnase I family were discovered, and termed “DNase1-like” proteins: Dnase1L1, Dnase1L2, and Dnase1L3
[8][9][10][11][12][13]. Dnase1-like 1 (Dnase1L1) was discovered in 1995 and first named human Dnase I lysosomal-like (DNL1L)
[8]. Dnase1L2 was first described in 1997, during the gene mapping of the Dnase1
[9]. Finally, Dnase1L3 was identified in 1994 from nuclei of rat thymocytes as the third of three nucleases and consequently termed ‘Dnase γ’
[12]. Dnase1L3 was also called novel human Dnase (nhDnase)
[13], and liver/spleen DNase (LS-Dnase)
[14].
Dnase1 family members often show restricted tissue expression. In humans, Dnase1 is primarily secreted in saliva, intestine, pancreas, kidneys, and urine, but is also present in serum
[1][15]. Dnase1L1 is restricted to skeletal muscle and cardiomyocytes
[16]. Dnase1L2 is primarily restricted to keratinocytes, and tissues containing them, like the skin
[17]. Dnase1L3 is secreted into blood, primarily by myeloid cells
[18]. Distinct Dnase1 family members enable tissue-specific DNA degradation, dependent on the function of that tissue. Overall, Dnases are essential for DNA degradation in most animals.